Welding apparatus



y 1951 s. M. HUMPHREY 2,553,970

WELDING APPARATUS Filed Dec. 22, 1942 2 Sheets-Sheet l gwucm/ om STANLEY M. HUMPHREY y 1951 s. M. HUMPHREY 2,553,970

WELDING APPARATUS Filed Dec. 22, 1942 2 Sheets-Sheet 2 Sumo/whom STANLEY M. HUMPHREY Patented May 22, 1951 UNITED STATES PATENT OFFICE 8 Claims. 1

This invention relates to electric welding apparatus of the capacitor discharge type and more particularly to such apparatus in which the capacitor discharge circuit is inductive thereby presenting the essential elements of an oscillatory circuit. The primary object of the present invention is the provision, in a welding system of this nature, of an arrangement whereby oscillation in the discharge circuit is avoided. This insures the uni-directional discharge of the capacitor through the welding load during a desired short interval of time and avoids the impression of damaging voltages of reversed polarity on the capacitor.

The present application is a continuation-inpart of applicants co-pending application Serial No. 379,084 filedFebruary 15, 1941, for Welding Apparatus, now U. S. Patent No. 2,436,863.

The inductive element of the discharge circuit comprises the primary winding of a transformer and by reason of the very heavy uni-directional surge of current resulting from the discharge of the capacitor the transformer, in systems of this nature, would normally become very quickly saturated thus rendering the translating apparatus substantially inoperative. To avoid this condition another important object of the invention is the provision of an arrangement whereby the charged capacitor is discharged through the welding transformer in alternate directions dur ing each succeeding welding operation. Thus any tendency of the welding transformer to saturate is neutralized and the involved welding system may therefore be operated at a high rate of production and over long periods of time without diminution of efficiency.

The reversal of current flow in the welding transformer may be accomplished either by employing a single section primary winding and reversing the current flow through this winding in each succeeding welding operation or by employing a two-section primary winding connected to the capacitor through suitable switching means which are controlled in such manner that the discharge current flows through opposite sections in each succeeding welding operation and in such direction as to provide effective reversals of the current flow with respect to the core of the transformer. In this embodiment, the required apparatus may be substantially simplified by providing the primary winding of the welding transformer with a center tap which may be permanently connected to one terminal of the capacitor thus providing the two sections mentioned and enabling the outer terminals of these 2 sections to be alternately connected to the opposite terminal of the capacitor with a minimum of apparatus.

The above and other objects and advantages of the invention will become apparent upon a consideration of the following detailed specification and the accompanyin drawing wherein there is specifically disclosed certain preferred embodiments of the invention.

In the drawing:

Figure 1 is a wiring diagram of a Welding system constructed in accordance with the principles of the invention; and

Figure 2 is a wiring diagram of a modified capacitor discharge circuit which may be substituted for the discharge circuit in the system in Figure 1.

Referring first to Figure 1, the line conductors LI and L2 constitute a suitable source of alternating current arranged to be connected to the primary of the transformer T2 through the contactors IF and 2F which are actuated by the relay coil F. For a purpose to be later described, the secondary winding of the transformer T2 may be constructed in such manner so as to provide a low impedance path between its output terminals. Also, the transformer T2 is preferably constructed in such manner so as to provide substantial leakage reactance between its primary and secondary windings to thereby limit the current translated. The principal or power capacitor of the system is indicated by the reference CDI and the welding transformer of the disclosed system by the reference T3. Current for control purposes is derived from the line Ll, L2 through the transformer T4, the conductors CL! and CLZ being connected to the terminals of the secondary winding of the transformer T4.

The secondary winding of transformer T2 is, in the preferred and illustrated embodiment of the invention permanently connected to the capacitor CDI through low impedance conductors and the rectifier TU and to provide for the control of the voltage to which the capacitor CDI is charged a sensitive relay SR is provided, the

operating coil of which is in series with the resistance 19 across the terminals of the capacitor CDI. Shunted across the coil is an adjustable resistance l5 which may be adjusted to cause operation of the relay at any predetermined voltage appearing across the capacitor CDI. The circuits controlled by the contacts on the relay SI are preferably supplied with direct current furnished by a dry disk type of rectifier RX which derives energy from the control current line through the transformer T5. Connected across the output of the rectifier RX through the conductors I3, I 1, contacts L and M of relay SR, and conductor is the coil of a relay Ri which is operative, when energized, to close its associated contactor and connect conductor 6 with conductor ll. Thus when the capacitor CD is discharged or has not attained the voltage for which resistance I5 has been adjusted the relay R1 is energized.

Coil F is in a. circuit leading from conductor CLI through conductors 2! and I5, contactor of relay RI, conductor ll, and conductor 28 through contactors 2B and 2G to line conductor GL2. Thus upon energization of relay Hi, the primary of transformer T2 is connected to the supply line Ll, L2 to charge the capacitor CDI. When the voltage on the capacitor reaches its proper value relay SR pulls in thus de-energizing coil F to interrupt the charging operation.

Capacitor CDI is arranged to be discharged through the primary winding of the transformer T3 through the conductors Ill and 12 in the latter of which is positioned the coil of a relay CR2. As shown in Figure l, the conductors ill and it are arranged to be connected to alternate terminals of the primary winding of the weldingtra-nsformer T3 by means of the double pole contactors Bl, B2 and Cl, C2 of the relays B and C, respectively. Relays B and C are arranged to be alternately actuated in each succeeding welding operation and it should be apparent that upon actuation of relay B, the current flow from capacitor CDI through the primary winding of transformer T3 is from right to left, as viewed in Figure 1, while actuation of relay C results in current flow in the opposite direction.

To provide for the alternate actuation of the relays B and C in the system illustrated, a relay ORA of the latch type is employed together with a latch release coil CRB. On the armature of the relay CRA is a normally open contactor CRAI and a normally closed contactor CRAZ. On the armature of the relay B are also the normally closed contactors IB and 2B and the normally open contactors B and 33. On relay C are also the normally closed contactors I C and 2C and the normally open contactors C and 3C.

Relay A is energized to initiate the discharge of capacitor CDI in each welding cycle and, as-

' suming the parts to be positioned as shown in Figure 1capacitor CDI being fully charged, the

. is energized through conductor 24 and contactor 3C and latches itself in while the holding contactor C on relay 0 insures continuation of energizati-on of its coil. Upon de-energization of relay A relay C drops out and upon the next succeeding energization of relay A the coil of relay B is energized through conductors 2i and 22, coil of relay B, contactors IC and CRAI and conductor 25 to conductor CL2. Relay B is thus energized to discharge capacitor CDI through the welding transformer T3 but in the opposite direction and coil CRB is energized through contactor 3B and conductor 25 to release relay CRA while holding contactor B insures continuation of energization of its coil upon opening of contactor 'CRAI. Thus the capacitor CDI is discharged through the welding transformer in alternate directions during each succeeding welding operation thereby avoiding magnetic saturation of the transformer.

In series with the operating coil of the relay A is a conductor 2l (leading from conductor CLl), the contactor of a relay R, conductor 28, a switch 29, and conductor 30 leading to conductor 0L2. Relay R is energized from the output of the rectified power supply RX through conduotors 33 and 34, contacts H and M of relay SR so that the capacitor CD! cannot normally be discharged until it has attained a predetermined voltage. Switch 29 may be either manually actuated or automatically actuated in response to the attainment of certain conditions required for the safe or satisfactory operation of the complete welding system such as welding pressure, for example. Normally, initiation of the complete welding cycle takes place periodically under the control of a timer, not shown, and in this case the switch 29 is closed and opened periodically provided the aforementioned conditions are properly attained.

shunting the switch 29 is a contactor CRZI so that the relay A will remain energized a supcient length of time to discharge the capacitor CD! even though the switch 29 is closed but momentarily, it being observed that the contactor CR2I is actuated and held closed by the current flowing in the conductor I2. As the welding current decreases beyond an effectual value contactor CR2i drops out thereby ole-energizing relay A. If desired, suitable time delay apparatus may be employed to delay the opening of relay A after the dropping of contactor CR2I. Likewise, if desired or necessary, suitable delaying means may be employed to retard the effect of the opening of relay R so that the energizing circuit for the relay A will not be interrupted during the discharge of capacitor CDI and the consequent dropping of the voltage thereof.

Upon actuation of either of the relays B or C, the charged capacitor CD5 is connected in series withthe inductive primary winding of the welding transformer T3 and normally the constants of this series circuit is such that oscillation tends to occur therein. To prevent this oscillation I employ a rectifier permanently connected across the principal power capacitor to provide a low impedance unidirectional current path in shunt with the capacitor to take the current flow resulting from the inductive reaction of the Welding transformer primary thereby avoiding the recharging of the capacitor and insuring the unidirectional discharge of the welding energy through the welding load. This is accomplished, in accordance with certain embodiments of the invention, by permanently connecting the charging rectifier to the capacitor and utilizing this same rectifier for both charging and the aforementioned shunt purposes. In one specific embodiment of the invention the secondary winding of the transformer which furnishes energy for charging the capacitor is constructed for low impedance and in this embodiment functions as one link in the aforementioned unidirectional shunt path. This embodiment is disclosed and claimed in the above mentioned co-pending application. In another specific embodiment of the invention an auxiliary contactor, herein'shown at A2, may be employed to close across the charging transformer secondary windings to avoid the requirement of special construction for said winding. As shown, contactor A2 is on relay A so that upon energization of this relay to effect the discharging of the capacitor through the welding load the secondary winding of the charging transformer T2 will be shunted by the low impedance circuit consisting of the conductor 35, contactor A2, and conductor 36. embodiment, the capacitor CD! is shunted directly by the rectifier (TU) independently of the charging transformer primary winding during the discharging of the capacitor through the welding load. This provides a direct uni-directional low impedance current path in shunt with the capacitor.

In practice, the transformer T2 and the rectifier TU may assume many difierent forms as will be readily understood by those skilled in the art. Likewise, the capacitor CDI may be replaced by a number of individual capacitors capable of being selectively connected in multiple to vary the total capacitance of the system.

Figure 2 illustrates a modified discharge circuit for the capacitor CDI. The welding transformer T6 is constructed with a primary winding having two sections 40 and 4| conveniently provided by employing a single center-tapped winding, as shown. This enables one of the conductors leading from the main capacitor, as the conductor IQ for example, to be permanently connected to the winding and allows the use of single pole switching devices to be employed to effect the desired alternate direction of current fiow. Thus, on relay B the double pole contactor BlB2 is replaced by a single pole contactor B3 while a single pole contactor C3 is substituted on the relay C. Conductor It is connected to one terminal of each of the sections 40 and M while the contactor B3 is operative, upon actuation of relay B, to connect the other terminal of section 49 to the other side of capacitor CD! through conductor I2. Likewise, contactor C3 is operative, upon actuation of relay C, to connect the other terminal of section M to the negative terminal of capacitor CDI through conductor 12.

Relays B and C, in the modification of Figure 2, are operated alternately in the manner described above in connection with Figure 1, the operating circuit being precisely the same in both embodiments, and it should be apparent that such alternate operation of these relays results in directing the flow of welding current through the transformer T6 in alternate directions in each succeeding welding cycle.

The above described embodiments of the invention should be considered as illustrative only as obviously many changes may be made therein without departing from the spirit or scope of the invention. The invention, therefore, is not to be restricted except insofar as required by the prior state of the art and the scope and extent of the appended claims.

I claim:

1. Welding apparatus comprising in combination a capacitor for storing welding energy, an alternating current source, means to charge said capacitor from said source comprising a transformer having its primary adapted to be connected to said source and its secondary connected to said capacitor through a rectifier, an inductive welding load circuit, means to discharge said capacitor through said load circuit, and means operative upon actuation of said means to discharge to provide a current conductive path in shunt with said secondary whereby during discharge of said capacitor said rectifier and said current conductive path provide a uni-directional Thus, in this current carrying path in shunt with said capacitor.

2. Welding apparatus comprising in combination a capacitor for storing welding energy, an alternating current source, means to charge said capacitor from said source comprising a transformer having its primary adapted to be connected to said source and its secondary connected to said capacitor through a rectifier, an inductive welding load circuit, means to discharge said capacitor through said load circuit, and means operative during discharge of said capacitor to connect said rectifier in shunt with said capacitor whereby during discharge of said capacitor said rectifier provides a direct uni-directional current path in shunt with said capacitor.

3. In an electric welding system of the capacitor discharge type having an inductive welding load circuit arranged to be energized by discharge of the capacitor the combination of means to charge said capacitor comprising a source of alternating current, a rectifier in series with said source and capacitor, means to discharge said capacitor through said circuit, and means operative upon actuation of said means to discharge to provide a. current conductive path across said source whereby during discharge of said capacitor said rectifier and current conductive path provide a uni-directional current carrying path in shunt with said capacitor.

4. In an electric welding system of the capacitor discharge type having an inductive welding load circuit arranged to be energized by discharge of the capacitor the combination of means to charge said capacitor comprising a source of a1- ternating current, a rectifier in series with said source and capacitor, and means to prevent oscillation in said load circuit during discharge of said capacitor comprising means providing a low impedance current path including said rectifier in shunt with said capacitor during the discharging of said capacitor.

5. Apparatus of the character described com-- prising in combination a capacitor, an alternating current source, means to charge said capacitor from said source comprising a rectifier, a load circuit, a transformer having a primary winding adapted to be energized by the discharge of said capacitor and a secondary winding connected to said load circuit, means to discharge said capacitor through said primary winding in alternate directions in succeeding impulses, and means c0mprising said rectifier to establish a uni-directional current path in shunt with said capacitor to prevent oscillation in the capacitor-primary winding circuit upon discharge of said capacitor.

6. Apparatus of the character described comprising in combination a capacitor, a load circuit, a transformer having a primary winding adapted to be energized by the discharge of said capacitor and a secondary connected to said load circuit, means to discharge said capacitor through said primary winding in alternate directions in succeeding operations, means responsive to the voltage on said capacitor to prevent operation of said discharge means unless said capacitor is charged to a predetermined voltage, and means comprising a rectifier to establish a uni-directional current path in shunt with said capacitor to prevent oscillation in the capacitor-prirnary winding circuit upon discharge of capacitor.

'7. Apparatus oi the character described comprising in combination a capacitor, a load circuit, a transformer having a primary winding adapted to be energized by the discharge of said capacfitcr and a secondary winding connected. to said load circuit, means to discharge said capacitor through said primary Winding, means responsive to the voltage on said capacitor to prevent operation of said. means to discharge unless said capacitor is charged to a predetermined voltage, and

means comprising a r ctifier to establish a unidirectional current path in shunt with said ca pacitor to suppress oscillation in the capacitor discharge circuit.

8. A condenser charging system comprising condenser, a source of alternating current, a rec- S relay, controlled means independent of the rectifier and responsive to the charge on said condense for deenergizing said relay when the charge on said condenser is above a predetermined level.

STANLEY M. HUMPHREY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,085,100 Knowles et a1. June 29, 1937 2,483,691 Dawson Oct. l, 1949 

